Why do I swell up during an allergic reaction?
Allergic reaction is a common finding in the ER. In some cases it can be a true, life threatening, emergency. The most severe type of allergic reaction is termed anaphylaxis and the resulting swelling or angioedema can be the life threatening symptom of said reaction.
Let’s start with some definitions and basic physiology. Most of us have either experienced an allergic reaction and angioedema or know someone who has.
As with most medical terms they describe exactly what we are talking about. Angio refers to our blood vessels and edema a swelling as a result of these blood vessels becoming too porous or “leaky.” Now when we say leaky we don’t mean red blood is coming out of the vessels. That would be termed hemorrhage.
In this case our vessels dilate to the point where only the smallest products of the blood are able to get out. These include water and small proteins. As an aside, histamine is one of the products released during this process. Histamine causes vessel dilation, bronchial constriction and in many cases severe itching. That’s why taking an antihistamine stops the itching in these cases.
As we can imagine if our vessels become larger or dilate and material begins to leak out, this can cause significant swelling at the site where this occurs. There are several conditions where this might occur. These conditions can involve vessels of a specific part of the body or generalized swelling throughout the body.
One of the first questions to ask, is why would our body want to do this?
The conventional answer is that when a specific area of our body suffers damage, infection or needs repair it needs to get the tools to repair the injury or fight the infection, to said site. This is done by sending white blood cells and other repair cells and proteins through our vessels to the effected site. Once these repair products get to the site in question they need to get outside of the vessel to repair the area in question.
To do this our vessels dilate and become leaky or porous. This is why any body who has sprained their ankle knows there is significant swelling to the hurt ankle. It’s not unlike a smoothly flowing interstate where suddenly the few cars wreck. Very quickly the interstate swells with emergency vehicles to provide support and care to the members of the accident.
Now that’s how angioedema is suppose to be helpful to us, at least, in theory.
Unfortunately, angioedema can occur when it is not supposed to, leading to dramatic and, sometimes, life-threatening situations.
One of the most common examples is an allergic reaction. In this case the body overreacts to a foreign body. The vessels dilate, the airways constrict and the blood pressure drops. This is all done in an attempt to rid the body of the unwanted visitor.
Unfortunately, in an attempt to bring help to the body our vessels can dilate to the point of blocking our airway. It doesn’t take an ER physician to realize this is not a good situation. In severe cases these patients require an emergency cricothyroidomy. This means the ER physician has to quickly cut a hole in the patient’s neck to provide oxygen to the lungs. This is neither fun for the patient or physician alike.
Fortunately, there are medications to help correct allergic reactions if caught before the patient loses his or her ability to breath.
Let’s keep in mind an allergic reaction is a broad spectrum depending on how severely the body reacts to the allergen. The term allergic reaction can mean anything from slight localized swelling or angioedema with itching only at the site of the allergen to full-fledged anaphylaxis where seconds separate a quick recovery from death.
The problem is a localized reaction can quickly advance to anaphylaxis. If you feel like you are beginning to have an allergic reaction get to the closest ER early!

Ask Dr Berry a question.
(dberrymd@hotmail.com)